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- Introduction to Vectors
- Vector vs Arrays
- Declaring and Initializing
- Adding Elements (push_back, emplace)
- Accessing and Modifying Elements
- Size, Capacity, and Resize
- Iterators and Traversal
- Conclusion
Introduction to Vectors
Vectors are a powerful and widely used component of the C++ Standard Template Library (STL). They are dynamic arrays that can grow or shrink in size automatically, unlike static arrays in C++. Vectors provide convenient functions and flexibility, making them ideal for modern C++ programming.
Vectors reside in the
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Vector vs Arrays
- Static vs Dynamic: Arrays have fixed sizes and must be defined at compile-time.Vectors can change size during runtime using methods like push_back() or resize().
- Ease of Use: Arrays require manual memory management. Vectors automatically manage memory, which reduces the risk of memory leaks or overflows.
- Functionality: Arrays lack built-in functions for sorting, insertion, or deletion. Vectors offer member functions for insertion, deletion, resizing, and more.
- Memory Efficiency: Vectors may allocate slightly more memory than needed to optimize resizing, but provide better real-world performance in dynamic scenarios.
Declaring and Initializing
To use vectors, include the
- #include
- std::vector
v1; // Empty vector of ints
- std::vector
v2(5); // Vector of 5 default-initialized ints (0)
- std::vector
v3(5, 10); // Vector of 5 elements, each initialized to 10
- std::vector
- int arr[] = {1, 2, 3, 4};
- std::
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Adding Elements (push_back, emplace)
- std::vector
v; - v.push_back(10);
- v.push_back(20);
- std::vector
- vp.emplace_back(1, 2); // Avoids copy, constructs pair directly
- v.insert(v.begin() + 1, 15); // Insert 15 at position 1
- std::vector
v = {1, 2, 3}; - v[0] = 10; // Direct access without bounds check
- std::cout << v[1];
- std::cout << v.at(2); // Throws std::out_of_range if index is invalid
- std::cout << v.front(); // First element
- std::cout << v.back(); // Last element
- std::cout << v.size();
- std::cout << v.capacity();
- v.resize(10); // Expands or reduces to size 10
- for (std::vector
::iterator it = v.begin(); it != v.end(); ++it) { - std::cout << *it << " ";
- }
- for (int x : v) {
- std::cout << x << " ";
- }
- for (auto rit = v.rbegin(); rit != v.rend(); ++rit) {
- std::cout << *rit << " ";
- }
push_back(): Adds an element to the end of the vector.
emplace_back(): Constructs an element in place at the end of the vector. Faster than push_back for objects.
insert(): Inserts at a specified position.
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Weekday / Weekend BatchesSee Batch DetailsAccessing and Modifying Elements
Using Index:
Using at():
Safer access with bounds checking.Front and Back:
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Size, Capacity, and Resize
size():Returns the number of elements.
capacity():Returns the allocated memory size (can be more than size()).
resize():Changes the size of the vector. Truncates or fills with default values.
shrink_to_fit():Reduces capacity to match size, freeing unused memory.
Iterators and Traversal
Iterators allow flexible and efficient traversal of vectors.
Basic Iterator Loop:
Range-based for Loop:
Reverse Iteration:
Conclusion
C++ vectors are one of the most versatile and efficient container types in the Standard Template Library. They offer dynamic sizing, rich functionality, and compatibility with powerful STL algorithms. From basic use cases like storing integers to complex operations like 2D matrix manipulation or sorting custom objects, vectors simplify coding and boost productivity. Understanding how to declare, modify, traverse, and optimize vectors is essential for writing modern C++ code. Whether you are preparing for interviews, working on software development, Adding Elements or diving into competitive programming, mastering vectors will significantly enhance your C++ skillset.
